Operational details of the ill-fated National Airlines Boeing 747-400 freighter which crashed on take-off from Bagram add further mystery to the reasons behind the fatal accident.

The aircraft had not been loaded at Bagram but at the UK base of Camp Bastion, outside of Lashkar Gah, some 600km to the southwest.

It had been transporting military vehicles out of Afghanistan, says the carrier, as well as other general freight.

Parent company National Air Cargo says that the freight inside the 747 had been "properly loaded and secured" and adds that it had "passed all necessary inspections" before leaving Camp Bastion.

This affirmation, and the fact that the aircraft apparently flew uneventfully to Bagram, might point away from a possible sudden shift of the freight on board the jet as it took off.

But the carrier also says that the 747 was refuelled at Bagram for its onward service to Dubai World Central as flight 102.

It has not indicated how much fuel was uplifted. Afghan investigators have yet to clarify the weight and balance status of the aircraft.

National Air Cargo notably says that no additional cargo was loaded at Bagram and that the freight being carried was inspected again before the departure.

Seven crew were on board - four pilots, two maintenance specialists and a loadmaster - but no-one had joined the flight at Bagram.

Surveillance data shows the aircraft operated from Hill AFB in Utah to Chateauroux, France, on 28 April before heading for Afghanistan. The crash occurred the following day.

Video of the accident shows the aircraft had been climbing out of the airport but appeared to lose forward airspeed before stalling and rolling into a steep right bank, then into a nose-down attitude. Although it rolled wings level, the aircraft failed to recover before striking the ground.

The video clearly shows the landing-gear deployed - probably indicating that the crew never managed to retract it after lift-off - as well as extended flaps.

None of the seven crew survived the impact, which occurred in close proximity to the high-elevation airport, which is sited some 1,500m (5,000ft) above sea level. NOTAM data warned that crash recovery operations were taking place 400ft northeast of Bagram's runway 03 overrun zone.

National Air Cargo says it "will not speculate" over the cause of the accident, adding that it will offer its "full co-operation" to the investigating authorities.

Source: Air Transport Intelligence news